1. Field of the Invention
The present invention relates to a propylene resin composition featuring excellent flexibility and transparency without producing sticky feeling.
2. Prior Art
The olefinic thermoplastic elastomers feature excellent balance between economy and properties, and have been extensively utilized for automotive parts such as bumpers and the like, as well as in the fields of a variety of industrial parts, household electric appliances, films and sheets, since they are light in weight and can be recycled.
So far, the olefinic thermoplastic elastomers have been produced by a mechanical mixing method in which ethylene-propylene rubber (hereinafter referred to as EPR) or ethylene-propylene terpolymer (hereinafter referred to as EPDM) and thermoplastic resins such as polypropylene, are kneaded together through an extruder, and a method (polymerization method) in which the two components are prepared through a series of polymerization operations to obtain a mixture of the two components. The production based on the polymerization method is generally a two-stage polymerization method in which the propylene is polymerized through the first stage, and the ethylene and propylene are copolymerized through the second stage.
However, the conventional EPR and EPDM produce sticky feeling. Moreover, the molded articles comprising a mixture thereof with polypropylene produce sticky feeling, too, and exhibit white color or milky white color. Therefore, they cannot be used as materials for the containers, sheets, films and the like that require transparency.
The thermoplastic elastomers produced by the polymerization method offer good transparency compared to those obtained through the mechanical mixing. However, the resins obtained by the polymerization method produce sticky feeling, too, and the molded articles thereof exhibit white color or milky white color, and cannot be used in the fields where transparency is required.
It has therefore been urged to develop a material that features good properties such as flexibility possessed by the above-mentioned mixture of EPR or EPDM and polypropylene, and offers excellent transparency without producing sticky feeling.
In order to solve the above-mentioned problems, Japanese Patent No. 2677920 and Japanese Unexamined Patent Publication (Kokai) No. 118354/1995 teach that a propylene copolymer having a particular composition features good flexibility and transparency.
However, the propylene polymer obtained by the above-mentioned method still contains low crystallinity components as well as amorphous components which produce the sticky feeling and impairs the transparency, still leaving room for improvement concerning the sticky feeling and transparency.